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JP2006270903

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DESCRIPTION JP2006270903
PROBLEM TO BE SOLVED: With the delay sum BF of the conventional filter design method (BF),
processing can be easily performed only with phase, but when the beam is wide, the peak
direction can not be guaranteed in the case of a sphere or unequally spaced array The side lobes
were getting bigger. SOLUTION: A coefficient of beam forming (BF) is redesigned according to an
input to realize high resolution beam forming (BF), and beam forming (BF) can be performed with
any microphone arrangement including a spherical array etc. Further, weights are calculated
based on the intensity distribution obtained by manipulating the beam direction of beam forming
(BF) according to equation 9, and beam forming (BF) is redesigned according to equation 10.
[Selected figure] Figure 1
Nonlinear beamforming with arbitrarily arranged microphone array
[0001]
The present invention relates to a method of designing a filter which forms a directional
characteristic by arranging a plurality of microphone arrays in an arbitrary space and combining
the output signals of the plurality of microphones.
[0002]
Conventionally, a method of recording a sound by providing a plurality of sound sensors with a
wide range of microphones (see Patent Document 1) and a search apparatus using a spherical
array transceiver (see Patent Document 2) have been disclosed. A method of forming a
directional characteristic by combining a plurality of microphone signals through a filter has
already been proposed.
04-05-2019
1
[0003]
And, a recording system (hereinafter referred to as SBM) realized by a microphone on a sphere
baffle has an advantage that the reflection and diffraction due to the microphone and its
supporting part can be reduced by embedding the microphone and its supporting part inside the
sphere. Although a method for forming a target directional characteristic has been proposed, the
filter design method used here is such that the relationship between the parameter value such as
the step size and the directional characteristic to be obtained is not clear because adaptive
processing is used. .
[0004]
Conventionally, control of directivity characteristics by a plurality of microphones is performed
as shown in FIG. 1 by setting N microphone signals X n (ω), n = 1, 2,. . . , N through a filter of
transfer characteristics Gn (ω) and processed so as to obtain a recorded signal Y (ω) having
directional characteristics, the distance r, azimuth angle θ, sound source X of elevation angle (
Assuming that the transfer function from ω) to microphone n is Hr, θ, ψ, n, (ω), the directivity
characteristic D (r, θ, 含 む) including the distance direction in this processing is given by the
following equation 15 It is a thing.
[0005]
[0006]
Next, subscripts m (m = 1, 2,.
In M), the following equation 16 is obtained.
[0007]
Number 16
d=Hg
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[0008]
In this case, d is a directional characteristic vector, H is a transfer function matrix, g is a filter
vector, and T is a transposed matrix, and the following equation 17 is obtained.
[0009]
[0010]
Then, as for the conventional filter design method not including adaptive processing, there is
delay sum beamforming (hereinafter BF), and if the filter gk in the target direction k is designed
by the following equation 18, the phase that cancels out the transmission phase delay It becomes
a filter with rotation, and * represents a complex conjugate.
[0011]
[0012]
Next, when the filter gk in the target direction k of the weighted delay sum BF is designed as +
with a pseudo inverse matrix and H with a Hermitian operator (complex conjugate transpose)
according to the following Eq. 19, each delay sum BF Of the filters with a gain proportional to the
transmission rate to the microphone, the gain in the direction k is 1 and the norm | gk | <2> is
the smallest, and | hm | is constant depending on the direction | Dm | <1 (m ≠ k), and the peak
is in the direction k, and in general, it is robust against fluctuation but has a wide directivity of
the side rope.
[0013]
[0014]
Next, a filter is designed to set the gain in the target direction k of the BF with NULL control to 1
and form NULL (gain 0) for non-target directions of N-1 or less, and the number of non-target
directions is L , Gku is designed by the following equation 20, assuming that the direction is ul (l
= 1, 2,..., L).
[0015]
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[0016]
Then, in the case of L (> N-1), the pseudo-inverse of the equation (20) can be calculated by the
inverse matrix, and if the non-purpose direction is appropriately selected, the siderope from the
delay sum BF at a particularly low frequency. Can form a directional characteristic in which the
[0017]
Furthermore, in LSE control BF, a filter that has a gain in the target direction k and keeps the
gain low with respect to the non-target direction of L = N−1 is designed. 1 for the target
direction and 0 for the non-target direction, but a filter of least square error (LSE) is designed,
and generally the gain in the target direction decreases when L is increased, in this case in the
target direction The weight w> 1 is added and the design can be relaxed by designing as the
following equation 21. If the non-target direction is appropriately selected, the side rope can be
suppressed to be low compared to the NULL control BF.
[0018]
[0019]
JP, 2002-48867, A JP, 2000-162308, A
[0020]
The delay sum BF of the conventional filter design method (BF) can be easily processed only with
the phase, but the beam is wide and the peak direction can not be guaranteed in the case of a
sphere or an uneven array The side lobe becomes large, and the weighted delay sum BF is strong
against the transfer function fluctuation, but the beam is wide and the side lobe becomes large.
Furthermore, in the BF with NULL control Although the direction of the side lobe can be set to 0,
only the number of microphones -1 can be set to 0, and the side lobe becomes large between the
positions set to 0. Furthermore, in the LSE control BF, Although the side lobes in multiple
directions can be made smaller, the height of the main beam is lowered, the gain in the target
direction is not guaranteed, and additionally, the peak position is not guaranteed either.
[0021]
In view of the above problems, the present invention is optimal based on each criterion in
beamforming (BF) in which the side rope (SL) is minimized in the LSE criterion and the Min-Max
criterion as a result of intensive research, so the main lobe ( Although it is impossible to further
reduce the side rope (SL) while keeping the ML) within a certain width, high resolution
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beamforming (BF) is required for applications such as sound source search, and the claims Nonlinear beamforming by the microphone array of arbitrary arrangement described in 1 goes
beyond the framework of linear processing, redesigns the coefficient of beamforming (BF)
according to the input, and realizes high resolution beamforming (BF). , Beam array (BF) with any
microphone arrangement including spherical array etc.
[0022]
Furthermore, in the non-linear beamforming by the microphone array in an arbitrary
arrangement according to claim 2, in the beamforming (BF) using the equation 9 according to
claim 1, when the intensity distribution of the sound source is unknown, the beamforming (BF) It
is optimal because it minimizes the expected value of the contribution (noise) of the output from
the non-target direction, but when the intensity distribution is known, the noise itself is added by
adding a weight proportional to the intensity. This can minimize the total noise by controlling the
gain in the non-target direction smaller by a strong noise source, and the intensity distribution is
often unknown in practice. Weights are calculated based on the intensity distribution obtained by
manipulating the beam direction of beam forming (BF) according to equation 9, and beam
forming (BF) is reestablished according to equation 10. And it performs, is similar to the general
adaptive microphone array, any of the microphone array becomes available, based beamforming
(BF) is one that may even not be NULL type.
[0023]
The non-linear beamforming by the microphone array of arbitrary arrangement of the present
invention redesigns the filter coefficient of beamforming (BF) according to the input signal,
thereby achieving high resolution and low resolution beyond the framework of linear fixed
beamforming (BF) It is a realization of the beam forming (BF) of the side rope.
[0024]
The non-linear beamforming by an arbitrary arrangement of microphone arrays according to the
present invention relates to a method of designing a filter for forming directional characteristics
by arranging a plurality of phone arrays in an arbitrary space and combining them through
output signals of the plurality of microphones. The beam forming (BF), which controls twodimensional directivity using SMA (Spherical Microphone Array) in which 31 microphones are
embedded in a sphere of 130 mm in radius, generates a sound source by scanning the beam
direction. Fig. 2 shows the results for a point source with the same intensity and phase at a
frequency of 1000 Hz as (θ, () = (0, 0) and (60, 0). Delay sum, (b) is the root mean square
minimum, (c) is beamforming (BF) with nonlinear optimization In (a), two sound sources can not
be separated, and one sound source appears. In (b), a horizontally long sound source appears,
and although the degree of separation is improved, it can not be said that it is sufficient. In c), the
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sound source can be completely recognized as two sound sources, and as for SL, (c) is small
compared to (b), and SL can be reduced while narrowing the width of ML.
[0025]
The present invention will be described in detail with reference to the drawings of an
embodiment of nonlinear beamforming by an arbitrary arrangement of microphone arrays
according to the present invention. FIG. 1 shows microphone directivity characteristics of the
embodiments of nonlinear beamforming by an arbitrary arrangement of microphone arrays of
the present invention. FIG. 2 is an explanatory diagram showing a processing system, and FIG. 2
is a weighted delay sum, (b) is a root mean square minimum, and (c) is a non-linear beamforming
embodiment according to the present invention. It is explanatory drawing showing the beam
forming (BF) by optimization.
[0026]
That is, as shown in FIG. 1, nonlinear beamforming by an arbitrary arrangement of microphone
arrays according to claim 1 of the present invention arranges a plurality of microphone arrays on
an arbitrary space and outputs signals from the plurality of microphones. Is a method of
designing a filter that forms a directional characteristic by combining them.
[0027]
Then, N microphones Mic. 1 to Mic. Signals X n (ω) from n, n = 1, 2,. . . , N through a filter of
transfer characteristics Gn (ω) and processed so as to obtain a recorded signal Y (ω) having
directional characteristics.
[0028]
Next, directional characteristics D (r, θ, including distance directions where the transfer function
from the sound source X (ω) from the elevation angle r to the microphone n is Hr, θ, ψ, n (ω)
ψ) is the following equation 22.
[0029]
[0030]
Then, the directions of the directions separated in the target range are subscripted m (m = 1, 2, ...
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When expressed as M), the equation 22 is represented by the equations 23 and 24.
[0031]
Further, assuming a directivity characteristic vector d, a transfer function matrix H, and a filter
vector g, the following equation 23 is obtained.
Number 23
d=Hg
[0032]
Furthermore, T can be expressed by the following equation 24 when expressed as a transposed
matrix.
[0033]
[0034]
Then, a filter gk in which the gain is 1 in the target direction k and the peak in the vicinity of the
target direction coincides with the target direction is defined as a solution of the following
equation 25: drhk, dθhk, dψhk, in equation 25 Is a vector whose elements are the differential
values at Hr, θ, ψ, n, (ω).
[0035]
[0036]
This solution is generally infinite with N> 4 and is given by the following equation 26.
[0037]
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[0038]
Here, gk is a solution satisfying the above equation 25, y is an arbitrary vector, and Z is a matrix
consisting of independent vectors spanning the null space of Hk.
[0039]
<img class = "EMIRef" id = "200753787-00000013" /> where Z is the singular value
decomposition of Hk Hk = U <1> SV <H> and the column vector of V corresponding to singular
value 0 Is obtained as
[0040]
[0041]
Next, when the gain u in the non-target direction is expressed by the equation 26, the following
equation 28 is obtained.
[0042]
[0043]
Here, u is a directional characteristic vector in the non-target direction, U is a transfer function
matrix in the non-target direction, and is given by the following equation 29.
[0044]
[0045]
<img class = "EMIRef" id = "200753787-000017" /> It is obtained by the equation 30.
[0046]
[0047]
<img class = "EMIRef" id = "200753787-000019" /> The diagonal matrix W is obtained by
finding a solution according to the following equation 31:
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[0048]
[0049]
<img class = "EMIRef" id = "200753787-000021" /> Substituting to find gk.
[0050]
Furthermore, in the non-linear beamforming by the arbitrary microphone array according to
claim 2 of the present invention, each of the non-linear beamformings using the arbitrary
microphone array according to claim 1 was beamformed using the equation 31 Assuming that
the matrix including the filter coefficients in the direction is Equation 32 and the input signal
vector is Equation 33, the sound source distribution s estimated from Equation 31 can be
calculated by Equation 34 using s = Gx.
[0051]
[0052]
Number 33
x=[X1X2… XN]<T>
[0053]
Number 34
s=[s1s2… sM]<T>
[0054]
Then, the weight Wm in the non-target direction can be calculated by the following equation 35.
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[0055]
Number 35
wm = | sm | + σ
[0056]
<img class = "EMIRef" id = "200753787-000023" />
[0057]
In the beamforming by microphones using indefinite terms according to the present invention, a
plurality of microphones are buried on the surface of a spherical baffle, and a filter is formed to
form directional characteristics by synthesizing through output signals of the plurality of
microphones. In beam forming (BF) where the side rope (SL) is the smallest in the LSE standard
and the Min-Max standard, the side rope (SL) is optimal based on each standard, so the main lobe
(ML) remains within a certain width. Although it is impossible to further reduce the rope (SL), in
applications such as sound source search, it provides high resolution beamforming (BF).
[0058]
FIG. 1 is an explanatory view showing a directivity characteristic processing system of a
microphone of an embodiment of nonlinear beam forming by an arbitrary arrangement of
microphone arrays according to the present invention.
Fig. 2 shows weighted delay sums (a) of the embodiments of nonlinear beamforming with
microphone arrays of arbitrary arrangement according to the present invention, (b) mean square
minimum, (c) beamforming (BF) by nonlinear optimization. FIG.
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